The present invention relates to anchor plates for use in anchoring waterproof roofing membranes.
Waterproof membranes are commonly used in the construction industry to cover roofs or line tunnels, swimming pools, tanks, waste pits and the like. When a membrane is laid down onto a surface, for the purpose of providing a waterproof covering, it is necessary to anchor the membrane to the surface to prevent it falling off or blowing off in the wind. For example, in a tunnel, the membrane is fixed to the inside of the tunnel rock walls and roof by anchors, and the concrete tunnel lining is applied over the membrane. The membrane prevents natural ground water from seeping through the concrete tunnel lining. On a roof, the membrane is held down by anchors fixed into the steel, concrete or wood substructure of the roof.
The anchor can take many forms, but the most important feature is not to exceed the point loading that will destroy the membrane during the anticipated maximum load conditions. These loading parameters are defined by national regulatory testing requirements, such as Factory Mutual in USA and LGA Tests in Europe. The way to reduce point loading is to use a number of anchors with a large attachment area, or many small area anchors spread evenly over the attachment area. This finally comes down to cost, either of the anchor itself, or of the labor to perform the attachment.
One form of known anchor is that shown in FIG. 1, in which a plastic or rubber pad 5, has been factory loaded with metallic granules in a suitable annular area 1. The top surface of the metallic loaded area is factory coated with a suitable adhesive 2 that will bond the pad to the underside of the membrane 3, when the adhesive is heated. A smaller plastic disc 4 is placed centrally over the pad 5 and is secured to the substructure 6 by means of a fixing device 7 (screw, nail, etc), passing through the center of the plastic disc 4. The substructure 6 may be covered with a layer of insulation 8. In use, an induction heater is applied above the membrane 3 to heat the metallic granules 1, which in turn heats the adhesive 2 thereby bonding the membrane 3 to the pad 5.
The benefits of this form of anchor are that the central fixing device 7 can be applied without due consideration of the small disc 4 becoming concave, due to being overdriven. Also, the flexible nature of the pad 5 allows the adhesive bond to flex and hence remain in the shear mode, so producing a far greater holding force.
The disadvantage is that it is more costly than other anchor systems. Furthermore, the membrane 3 is not fixed directly to the disc 4 therefore it may flap in the wind and variations in ambient temperature which cause the membrane 3 to shrink and expand can cause damage to the pad 5, where the fixing device 7 passes through, causing failure of the pad 5 by tearing. A further problem exists if the surface under the pad 5 is not uniformly flat, in that the heating of the metallic granules 1 will be uneven, causing a failure potential.
FIG. 2 shows another form of known anchor plate comprising a steel plate 9 which has a factory bonded layer of membrane material 10 on its upper surface. This anchor plate is fixed to the substructure 6 by a fixing device 7 which passes through the center of the anchor plate. The anchor plate 9 has a countersink 14 in the center to accommodate the head of the fixing device 7, so that the top profile of the anchor plate, over the surface of the membrane material 10 is totally flat with the top of the fixing device 7 in place. The substructure 6 may be covered with an insulating layer 8. The overlying membrane 3 is secured to the anchor by means of applying a solvent 12 to the upper surface of the material 10 and then quickly applying pressure to top of the membrane 3 to initiate the bonding procedure.
The benefits of this anchor system is that it is simple and low cost and it anchors the membrane 3 securely to the substructure 6.
The disadvantages are that the solvent application is very unhealthy for the operator and if the fixing device 7 is overdriven, the anchor plate will become concave. This both weakens it for vertical wind loading and makes it difficult to obtain a uniform bond with the solvent, unless the membrane 3 is held down into the concavity until the solvent sets.
A simple new anchor system was required to overcome these difficulties, especially the solvent use.
EP 0735210 describes a disc very similar to FIG. 2, but without the factory bonded membrane material as shown in FIG. 3. A steel anchor plate 9 has a countersink 14 in the center to accommodate the head of the fixing device 7 so that the top profile of the anchor plate is totally flat with the top of the fixing device 7 in place. The thickness of the steel anchor plate 9 was increased until the top surface would not become concave if the fixing device 7 was overdriven. The anchor plate is fixed to the substructure by the fixing device 7. The substructure may be covered by a layer of insulation 8. The top surface of the anchor plate 9 is factory coated with a suitable heat activated adhesive 13. The induction heater is applied above the membrane 3 and is used to heat the steel anchor plate 9 which in turn heats the adhesive 13 which then bonds the steel anchor plate 9 to the membrane 3.
The benefit of this anchor plate is its simplicity.
The main disadvantage of this plate is that even when the steel thickness is substantial, the top surface of the plate still becomes slightly concave when the fixing device 7 is overdriven. The reason being that the countersink 14 part of the plate has to be driven down into the insulation layer 8, so that the bottom surface of the anchor plate sits on the surface of the insulation layer 8. Further disadvantages are that the increased thickness of the steel increases the cost of the anchor plate and the considerable thickness of the steel requires much more heat time from the induction heater, resulting in increased costs. Another disadvantage of this design is that it cannot be used in applications where there is no insulation layer to accept the countersink part of the anchor plate.
It is thus an object of the present invention to provide an anchor plate which overcomes or alleviates the drawback of the known anchor plates.
In accordance with one aspect of the present invention there is provided an anchor plate for securing a membrane to a structure, the plate comprising a first part for receiving a fastener for connecting the plate to the structure and which has a fastening area which contacts the structure and a second part which is elevated with respect to the fastening area for contacting the membrane and which second part carries a heat activated adhesive.
This has the advantage that when the plate is secured to a structure, the height difference between the bonding area and the fastening area leads to a reduction in the force applied to the bonding area when a fastener is inserted into the plate in order to secure the plate to the structure, with a consequent reduction in the distortion of the bonding area allowing the bonding area to retain its proper shape for its intended use. The increased strength of the plate structure leads to a reduction in the amount of material required for its construction with a consequential reduction in unit cost. Also, because the plate is more visible when covered by a membrane, this allows its easier location for heat activation of the adhesive.
Preferably, the first part has a substantially planar base for contacting the support. The planar undersurface of the fastening part leads to a stable support for the anchor plate to sit on in the event that the plate is mounted to a solid substructure, further reducing the curvature of the upper bonding surface.
Preferably, the first part is flexible. This allows the support contacting surface to more readily adapt to the profile of a non-uniform support, further reducing distortion to the plates bonding area and also providing tactile feedback to the user which prevents overdriving of the plate into a less solid surface, such as an insulating layer.
In a preferred embodiment the first part is an insert. This has the advantage that a variety of fastening means can be used with a particular plate design by simply inserting the insert which is adapted to receive the desired fastening device. Thereby manufacturing costs are reduced because only one set of tooling is required to produce the plate rather than a plurality of tooling adapted to produce a respective plurality of plates each with means to receive a different fastener.
The insert may be a plastics disc. This has the advantage that it is relatively cheap to make alternative plastics inserts to receive the head shape of any required fastener. If the anchor plate is used in a cold climate and the fastener passes through an insulation layer into a warm moist environment below the substructure, the fastener can lose heat to the atmosphere, which causes moisture to condense on the fastener and corrosion to set in, ultimately resulting in failure. The plastics insert has the advantage that it provides a high degree of thermal insulation for the fastener and thereby reduces corrosion and potential failure thereof.
The second part is elevated with respect to the fastening area and the insert may fill the void within the bonding area. This has the advantage that this prevents the membrane sinking down onto the head of the fastener and forming a depression that traps dirt and rain water. The load carrying limit of the plate is set by the force that fixes the fastener in place. The insert provides a larger quantity of material about the fastener""s head further reducing stress during insertion of the fastener and allowing a greater load carrying limit for the plate.
Preferably the first part is corrugated. This has the advantage of strengthening the fastening area, thereby better absorbing the fastening force and reducing any distortion in use extending to the elevated bonding area.
Preferably, the first part comprises a raised area providing a countersink for receiving a fastener.
Preferably, the first part comprises a central opening for receiving a fastener and the second part is annular and coaxial with said opening.
Preferably, the first part carries a heat activated adhesive. This has the advantage that in use the fastener can be secured by the plate, when the membrane is bonded to the plates second part.
In a preferred embodiment the plate includes at least one third part forming a support for the plate, the second part being elevated with respect to the third part and the third part being remote from the first part. This has the advantage that the plate can be more securely balanced on an underlying structure, reducing tilting of the plate in use if an edge thereof is trodden on. Furthermore the support increases the rigidity of the second part reducing the influence of wind, if for example the plate is used on a roof and reducing the tendency for the plate to bend if a membrane is hung therefrom for example in a tunnel.
Also, the turned down edges provides better retention of insulation boards, with the plate both securing the overlying membrane and securing the underlying insulation boards without the need for additional fixing means. The bending of the surface also produces a smooth edge which reduces tearing of the membrane when it is pulled over the plate.
Preferably the third part has a substantially planar base, more preferably the third part""s planar base is co-planar with the planar base of the first part. This facilitates the use of the plate on a planar structure.
In a preferred embodiment the third part surrounds the second part.
Preferably a frustoconical surface extends between the first and second parts and/or the second and third parts.
Preferably, the anchor plate is stamped from a sheet of steel.
Preferably, the anchor plate is non-metallic and includes metallic granules.
In accordance with a second aspect of the present invention, there is provided an anchor plate for securing a membrane to a support, the plate being coated on its side adapted to contact the support with a heat activated adhesive.
Preferably the anchor plate also comprises means for the attachment of a separate fastening means.
Preferably both sides of the plate carry a heat activated adhesive, more preferably the opposite sides of the plate carry different adhesives.
Preferably, the anchor plate is metallic.
Preferably, the anchor plate is non-metallic and includes metallic granules.